Boron nitride nanotubes enable room-temperature quantum tunneling

Published on July 1st, 2013 | By: Jim Destefani

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Electrons “tunnel” one at a time across a series of gold quantum dots deposited on BNNTs. The room-temperature tunneling device behaves like a transistor but contains no semiconductors. Credit: Yoke Khin Yap/MTU

Transistors have come a long way since their development at Bell Labs and first commercial success at the core of portable, battery-powered radios like those shown above. (These are part of an ACerS colleague’s colllection.)

Transistors, of course, are also at the heart of the integrated circuits used in any kind of computerized device. Back in 1965, a man named Gordon Moore—one of the founders of chip making giant Intel—postulated that the number of transistors on integrated circuits would double approximately every two years. “Moore’s Law” has turned out to be quite an accurate predictor of IC technology development ever since, perhaps because Intel and other manufacturers have used its central tenet as a target for innovation. As a result, it’s now routine for companies like Intel to make devices with tens or even hundreds of millions of transistors on a single silicon chip.

But current chipmaking technology and materials are starting to bump into the lower size limits of what they can achieve, prompting many researchers to ask what’s next in transistor technology. One answer comes from a group at Michigan Technological University (Houghton), who have been collaborating with workers at Oak Ridge National Laboratory to develop nanoscale transistor technology.

“The idea was to make a transistor using a nanoscale insulator with nanoscale metals on top,” said MTU researcher Yoke Khin Yap in a news release. The insulator in this case was boron nitride nanotubes, akin to carbon nanotubes but more difficult to synthesize and work with, according to this 2010 release.

What eventually emerged from the MTU lab was a device that consists of a “carpet” of BNNTs topped with laser-deposited gold quantum dots only 3 nm across. When a voltage was applied to the device, electrons flowed from dot to dot in a phenomenon known as quantum tunneling.

According to Michigan Tech physicist John Jaszczak, the big news is the device’s ability to exhibit quantum tunneling behavior at room temperature. Other tunneling devices “only operate at liquid-helium temperatures,” he said.

Jaszczak attributed the room-temperature tunneling phenomenon to the device’s tiny size—about one micron long and about 20 nm wide, according to the release. “The gold islands have to be on the order of nanometers across to control the electrons at room temperature,” he said. “If they are too big, too many electrons can flow. “Working with nanotubes and quantum dots gets you to the scale you want for electronic devices.”

Yap has filed for international patents on the technology. “Theoretically, these tunneling channels can be miniaturized into virtually zero dimension when the distance between electrodes is reduced to a small fraction of a micron,” he said.

The work is fully reported in an article recently published online in Advanced Materials.